<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">

    <title></title>
    <style>
        #parent{
            display: flex;
            justify-content: center;
        }
        .son{
            background-color: #00ff00;
        }
    </style>
</head>
<body>

<div id="parent">
    <div class="son">
        儿子
    </div>
    <div class="son">
        儿子
    </div>
    <div class="son">
        儿子
    </div>
</div>
</body>
</html>